package com.teamsun.util;

import java.io.ByteArrayOutputStream;

/**
 * <p>base64解密</p>
 * <p>前台传入的参数会使用base64加密,该类提供解密方法</p>
 */
public class Base64Util {
    private static char[] base64EncodeChars = new char[] { 'A', 'B', 'C', 'D',
            'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q',
            'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
            'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',
            'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3',
            '4', '5', '6', '7', '8', '9', '+', '/', };

    private static byte[] base64DecodeChars = new byte[] { -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59,
            60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
            10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1,
            -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37,
            38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1,
            -1, -1 };

    /**
     * base64±àÂë
     * @param {Object} str
     */
    public static String base64encode(String param){
        int c1, c2, c3;
        int len = param.length();
        int i = 0;
        String out = "";
        while (i < len) {
            c1 = param.charAt(i++) & 0xff;
            if (i == len) {
                out += base64EncodeChars[(c1 >> 2)];
                out += base64EncodeChars[((c1 & 0x3) << 4)];
                out += "==";
                break;
            }
            c2 = param.charAt(i++);
            if (i == len) {
                out += base64EncodeChars[(c1 >> 2)];
                out += base64EncodeChars[(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4))];
                out += base64EncodeChars[((c2 & 0xF) << 2)];
                out += "=";
                break;
            }
            c3 = param.charAt(i++);
            out += base64EncodeChars[(c1 >> 2)];
            out += base64EncodeChars[(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4))];
            out += base64EncodeChars[(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6))];
            out += base64EncodeChars[(c3 & 0x3F)];
        }
        return out;
    }

    /**
     * 解密
     * @param str
     * @return
     */
    public static byte[] decode(String str) throws Exception{
        byte[] data = str.getBytes();
        int len = data.length;
        ByteArrayOutputStream buf = new ByteArrayOutputStream(len);
        int i = 0;
        int b1, b2, b3, b4;

        while (i < len) {
            do {
                b1 = base64DecodeChars[data[i++]];
            } while (i < len && b1 == -1);
            if (b1 == -1) {
                break;
            }

            do {
                b2 = base64DecodeChars[data[i++]];
            } while (i < len && b2 == -1);
            if (b2 == -1) {
                break;
            }
            buf.write((int) ((b1 << 2) | ((b2 & 0x30) >>> 4)));

            do {
                b3 = data[i++];
                if (b3 == 61) {
                    return buf.toByteArray();
                }
                b3 = base64DecodeChars[b3];
            } while (i < len && b3 == -1);
            if (b3 == -1) {
                break;
            }
            buf.write((int) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));

            do {
                b4 = data[i++];
                if (b4 == 61) {
                    return buf.toByteArray();
                }
                b4 = base64DecodeChars[b4];
            } while (i < len && b4 == -1);
            if (b4 == -1) {
                break;
            }
            buf.write((int) (((b3 & 0x03) << 6) | b4));
        }
        return buf.toByteArray();
    }


    /**
     * 返回解密结果
     */

    public static String decodeToString(String param) throws Exception{
        return new String(decode(param));
    }

    public static void main(String[] args) throws Exception {
        String encode = base64encode("shHRAccessInReport");
        System.out.println(encode);
        System.out.println(decodeToString(encode));
    }
}
